I agree that he was acting like an idiot with the senpai but it's super stupid the sister situation, I'm sorry but that's kinda the point, you think he would care about an stupid concert when his sister is sick.
This is not a matter of it being something he should feel bad about this is something that he did out of care for his sister, the senpai situation is true he did it for his own situation(tho i have to say if he said he did it because he is just shy and doesn't like the attention it be fine by me, sometimes people can't just ignore others, it's not that easy and caring about it is normal).
He was wrong to not talk it but the sister situation is stupid and a horrible way to explain it or show the message